Newton's Laws: Inertia, F=ma, and Third Law

Inertia

  • Net force zero ⇒ constant velocity
  • Equation: ∑F=0⇒a=0\sum \mathbf{F} = 0 \Rightarrow \mathbf{a} = \mathbf{0}

F = ma

  • Net force determines acceleration
  • Equation: ∑F=ma\sum \mathbf{F} = m \mathbf{a}
  • Alternative: a=∑Fm\mathbf{a} = \frac{\sum \mathbf{F}}{m}

Pairs

  • Action–reaction: forces are equal in magnitude and opposite in direction on two bodies
  • Explains interactions (rockets, pushes)